As a drive unit includes an electric motor which operates as a generator during braking or when travelling downhill and generates an electric current, there must be a braking resistor, known per se. This converts the electrical energy which is not required and which is associated with this current into thermal energy.
Hitherto it was customary to position the braking resistor on the locomotive, specifically in contact with the ambient air, in order to ensure sufficient cooling of the braking resistor.
It is also known that an internal combustion engine, for example a diesel engine, has to be cooled while it is operating. The diesel engine which is generally used in a diesel-electric motor is connected to a cooling system which holds a fluid, for example water. This cooling system includes a cooling circuit. The liquid has to have specific minimum temperature in order to ensure low-wear starting of the diesel engine, even when the locomotive is switched off. For this reason, hitherto, when the outside temperatures were very low, the diesel engine was operated continuously in the idling mode, even in a locomotive which was stationary for a relatively long time period.
On very long parts of routes with gradients, which result in the electric motor of the drive unit operating for a very long time as a generator, the braking resistor must convert the very large amount of electrical energy into heat. There is therefore a need for a very large braking resistor or a complex blower to conduct away the heat more quickly.